On Tue, 2014-07-15 at 18:50 +0200, Ard Biesheuvel wrote: > The EFI loader may load Image at any available offset. This means Image may > reside very close to or at the base of DRAM, in which case the relocation > done by efi_entry() results in Image being moved up in memory, which is > undesirable (memory below the kernel is currently not usable). > > To work around this, we check in the stub whether the relocated offset is higher > than the original offset. If this is the case, the original and relocated Images > switch roles, and we move the original Image inside its original lower mapping > while executing from the relocated Image. > > To ensure the original mapping has sufficient size, we add 2 megs + TEXT_OFFSET > of padding to the PE/COFF .text section, this should be sufficient to cover > rounding and adding TEXT_OFFSET. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > --- > > This was tested on a Foundation Model using the patch below, which forces the > Image to be loaded at 0x80000000 (base of DRAM). > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 2b7bd5eff776..eeadc073bad3 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -138,12 +138,12 @@ pe_header: > .short 0 > coff_header: > .short 0xaa64 // AArch64 > - .short 2 // nr_sections > + .short 1 // nr_sections > .long 0 // TimeDateStamp > .long 0 // PointerToSymbolTable > .long 1 // NumberOfSymbols > .short section_table - optional_header // SizeOfOptionalHeader > - .short 0x206 // Characteristics. > + .short 0x207 // Characteristics. > // IMAGE_FILE_DEBUG_STRIPPED | > // IMAGE_FILE_EXECUTABLE_IMAGE | > // IMAGE_FILE_LINE_NUMS_STRIPPED > @@ -158,7 +158,7 @@ optional_header: > .long stext_offset // BaseOfCode > > extra_header_fields: > - .quad 0 // ImageBase > + .quad 0x80000000 // ImageBase > .long 0x20 // SectionAlignment > .long 0x8 // FileAlignment > .short 0 // MajorOperatingSystemVersion > @@ -193,6 +193,7 @@ extra_header_fields: > // Section table > section_table: > > +#if 0 > /* > * The EFI application loader requires a relocation section > * because EFI applications must be relocatable. This is a > @@ -212,6 +213,7 @@ section_table: > .long 0x42100040 // Characteristics (section flags) > > > +#endif > .ascii ".text" > .byte 0 > .byte 0 > > > arch/arm64/kernel/Makefile | 1 + > arch/arm64/kernel/efi-entry.S | 48 +++++++++++++++++++++++++++++++++---------- > arch/arm64/kernel/head.S | 7 ++++--- > 3 files changed, 42 insertions(+), 14 deletions(-) > > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > index cdaedad3afe5..d55da3cd8a97 100644 > --- a/arch/arm64/kernel/Makefile > +++ b/arch/arm64/kernel/Makefile > @@ -6,6 +6,7 @@ CPPFLAGS_vmlinux.lds := -DTEXT_OFFSET=$(TEXT_OFFSET) > AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) > CFLAGS_efi-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET) \ > -I$(src)/../../../scripts/dtc/libfdt > +AFLAGS_efi-entry.o := -DTEXT_OFFSET=$(TEXT_OFFSET) > > CFLAGS_REMOVE_ftrace.o = -pg > CFLAGS_REMOVE_insn.o = -pg > diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S > index a0016d3a17da..d154f3c73937 100644 > --- a/arch/arm64/kernel/efi-entry.S > +++ b/arch/arm64/kernel/efi-entry.S > @@ -11,6 +11,7 @@ > */ > #include <linux/linkage.h> > #include <linux/init.h> > +#include <linux/sizes.h> > > #include <asm/assembler.h> > > @@ -45,10 +46,13 @@ ENTRY(efi_stub_entry) > * efi_system_table_t *sys_table, > * unsigned long *image_addr) ; > */ > - adrp x8, _text > - add x8, x8, #:lo12:_text > + adrp x22, _text > + add x22, x22, #:lo12:_text // x22: base of Image Why change x8 to x22? Seems unnecessary. Not only that, it is callee-saved, but you don't save it. This could cause a problem if boot fails and we try to return to firmware. > + adrp x24, _edata > + add x24, x24, #:lo12:_edata > + sub x24, x24, x22 // x24: size of Image Should use a caller-saved register instead of x24. > add x2, sp, 16 > - str x8, [x2] > + str x22, [x2] > bl efi_entry > cmn x0, #1 > b.eq efi_load_fail > @@ -61,19 +65,41 @@ ENTRY(efi_stub_entry) > */ > mov x20, x0 // DTB address > ldr x0, [sp, #16] // relocated _text address > - ldr x21, =stext_offset > - add x21, x0, x21 > + ldr x23, =stext_offset > + add x21, x0, x23 > > /* > + * Check whether the original allocation done by the EFI loader is more > + * favorable (i.e., closer to the base of DRAM) than the new one created > + * by efi_entry(). If so, reuse the original one. > + */ > + adr x3, 0f > + cmp x3, x0 > + bgt 1f // this image is loaded higher, so just proceed normally > + > + /* > + * Jump into the relocated image so we can move the original Image to > + * a 2 MB boundary + TEXT_OFFSET inside the original mapping without > + * overwriting ourselves. > + */ > + sub x3, x3, x22 // subtract current base offset > + add x3, x3, x0 // add base offset of relocated image > + br x3 // jump to next line, but in relocated image > + > +0: mov x1, x0 // copy from relocated Image > + sub x0, x22, #1 // copy to base of original Image > + orr x0, x0, #(SZ_2M - 1) // .. rounded up to 2 MB > + ldr x3, =(TEXT_OFFSET + 1) // .. plus TEXT_OFFSET > + add x0, x0, x3 > + mov x2, x24 // copy 'size of Image' bytes > + bl memcpy > + add x21, x0, x23 // add stext_offset to entry point > +1: > + /* > * Flush dcache covering current runtime addresses > * of kernel text/data. Then flush all of icache. > */ > - adrp x1, _text > - add x1, x1, #:lo12:_text > - adrp x2, _edata > - add x2, x2, #:lo12:_edata > - sub x1, x2, x1 > - > + mov x1, x24 // size of Image > bl __flush_dcache_area > ic ialluis > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 5cd1f3491df5..2b7bd5eff776 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -129,6 +129,7 @@ efi_head: > #endif > > #ifdef CONFIG_EFI > +#define PE_TEXT_PAD SZ_2M + TEXT_OFFSET > .globl stext_offset > .set stext_offset, stext - efi_head > .align 3 > @@ -150,7 +151,7 @@ optional_header: > .short 0x20b // PE32+ format > .byte 0x02 // MajorLinkerVersion > .byte 0x14 // MinorLinkerVersion > - .long _edata - stext // SizeOfCode > + .long _edata - stext + PE_TEXT_PAD // SizeOfCode > .long 0 // SizeOfInitializedData > .long 0 // SizeOfUninitializedData > .long efi_stub_entry - efi_head // AddressOfEntryPoint > @@ -168,7 +169,7 @@ extra_header_fields: > .short 0 // MinorSubsystemVersion > .long 0 // Win32VersionValue > > - .long _edata - efi_head // SizeOfImage > + .long _edata - efi_head + PE_TEXT_PAD // SizeOfImage > > // Everything before the kernel image is considered part of the header > .long stext_offset // SizeOfHeaders > @@ -215,7 +216,7 @@ section_table: > .byte 0 > .byte 0 > .byte 0 // end of 0 padding of section name > - .long _edata - stext // VirtualSize > + .long _edata - stext + PE_TEXT_PAD // VirtualSize > .long stext_offset // VirtualAddress > .long _edata - stext // SizeOfRawData > .long stext_offset // PointerToRawData -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
